Process for purifying and recovering catalyst solution contaminated during the carbonylation of methyl acetate and/or dimethylether

Abstract

Catalyst solution contaminated during the carbonylation of methyl acetate and/or dimethylether. To this end, the contaminated catalyst solution is subjected in a first processing stage to extraction with a dialkylether and alkanol, each of which has from 1-4 carbon atoms per alkyl group, and thereby freed from its organic contaminants, from acetic acid, acetic anhydride and ethylidene diacetate, and the ether phase is separated from the purified promoter-containing catalyst solution; next, the ether phase is treated in a second processing stage with iodine and/or methyl iodide; the precipitated promoter containing catalyst complex is separated and dissolved in the purified catalyst solution coming from the first processing stage; the ether phase is separated into its constituents by distilling it; recovered dialkylether and alkanol are used again in the extraction stage; fresh catalyst solution is prepared from the recovered mixture of acetic acid, acetic anhydride and ethylidene diacetate and from the united purified catalyst solution while residual dialkylether and alkanol are distilled off, and the organic contaminants retained in the residue of the ether phase distillation are expelled.

We claim: 
     
       1. A process for purifying and recovering catalyst solution contaminated during the carbonylation of methyl acetate, dimethylether, or a mixture thereof, containing carbonyl complexes of rhodium, quaternary heterocyclic aromatic nitrogen compounds or quaternary organophosphorus compounds as organic promoters, or alkali metal salts or compounds of a carbonyl-yielding non noble metal as inorganic promoters, or a mixture of the said organic and inorganic promoters, undistillable organic contaminants as well as acetic acid, acetic anhydride and ethylidene diacetate, which comprises: subjecting the contaminated catalyst solution in a first processing stage to extraction with a dialkylether and alkanol, each of which has from 1-4 carbon atoms per alkyl group, 0.5 to 20 parts by weight dialkylether and 0.03 to 0.4 part by weight alkanol being used per part by weight contaminated catalyst solution, thereby freeing said contaminated catalyst solution from its organic contaminants, from acetic acid, acetic anhydride and ethylidene diacetate, and separating an ether phase from a purified promoter-containing catalyst solution; treating the ether phase in a second processing stage with iodine and/or methyl iodide; separating precipitated promoter-containing catalyst complex and dissolving said precipitated promoter-containing catalyst complex in the purified catalyst solution coming from the first processing stage to form a united purified catalyst solution; separating the ether phase into its constituents by distilling it; using recovered dialkylether and alkanol again in the extraction stage; preparing fresh catalyst solution from the recovered mixture of acetic acid, acetic anhydride and ethylidene diacetate and from the united purified catalyst solution and distilling off residual dialkylether and alkanol from the fresh catalyst solution and discarding the organic contaminants retained in the residue of the ether phase distillation. 
     
     
       2. A process as claimed in claim 1, wherein the contaminated catalyst solution is extracted with the dialkylether and alkanol, and the ether phase is treated with iodine and/or methyl iodide at temperatures of from 5° to 140° C. and under pressures of from 1 to 30 bars. 
     
     
       3. A process as claimed in claim 1, wherein 0.00005 to 0.01 part by weight iodine and/or methyl iodide is used per part by weight dialkylether. 
     
     
       4. A process as claimed in claim 1, wherein at least one alkanol is added in the first processing stage to the contaminated catalyst solution or dialkylether. 
     
     
       5. A process as claimed in claim 1, wherein the contaminated catalyst solution is distillatively freed initially from volatile acetic acid, acetic anhydride and ethylidene diacetate, the distillation residue is then extracted with the dialkylether and alkanol, and the resulting two phase mixture is separated into purified, promoter-containing catalyst solution and into an ether phase containing organic contaminants.